The computerized networks used by fourth-generation (4G) mobile terminals comprise radio sub-networks, sometimes designated by the initials RAN for “Radio Access Network”, which are hooked up to an interconnection network, also called a CSN (“Connectivity Service Network”), the CSN being linkable to the Internet. A fourth-generation mobile terminal is identified by an IP (“Internet Protocol”) address which allows it to receive and to send data across the whole of the computerized network. The mobile terminal is under the coverage of an antennal station, also called a base station. A RAN is formed of a set of base stations whose coverages supplement one another so as to cover a territory. Between the mobile terminal and the base station, the data are transmitted in the form of radioelectric waves and then the base station transmits the data, generally via optical fibers or cables, to a gateway interfacing between a RAN and a CSN. As a general rule, several base stations are controlled by one and the same control station. Such a control station fulfills several roles, notably the filtering of packets, the management of service quality, the authentication of users, the control of the base stations.
When the mobile terminal moves and exits the zone covered by a first base station under the coverage of which it was situated, the communications are ensured by a second base station whose coverage is adjacent to the first. If the second base station is connected to the same control station as the first base station, one speaks of micro-mobility. In the case where the mobile terminal moves to a second base station which is connected to a control station different from the first control station, the term macro-mobility is employed. The present invention deals more particularly with problems of continuity of communications within the framework of the macro-mobility of mobile terminals.
A protocol, called MIP for “Mobile IP”, is known for managing the macro-mobility of mobile terminals on WiMax networks. MIP relies on the HA (“Home Agent”) and FA (“Foreign Agent”) functions which are software modules executed by routers at the level of the IP network layer (layer 3). The HA function makes it possible to receive and to steer data packets intended for the mobile terminal, including when the latter leaves its initial gateway. The FA function is executed by a router for relaying the data packets up to the mobile terminal. The HA function is an anchoring point for the mobile terminal in the CSN and this anchoring point persists as long as the mobile terminal is under the coverage of a RAN, whatever the base station to which it is connected. The HA function is generally executed by a single router of the CSN and thus constitutes a significant point of weakness. Hence, if a movement of the mobile terminal entails a change of control station, and if the router executing the HA function is not reachable from the new gateway—for example, if several communication links are cut—, the communication may not be maintained, despite the optional duplication mechanisms implemented. Hence, although the MIP protocol can constitute a solution in a centralized environment, it is not suited to networks with strong reliability constraints, such as for example private mobile radio or PMR.
A technique described in the French application published under the number FR2953357 has already been proposed for solving the problems of macro-mobility in a context of high reliability. However, this technique is less optimized when the interconnection network operates at the level of the IP layer, that is to say when the network uses IP routers rather than level-2 Ethernet switches.